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barrysloateCorey makes a great point, and given that a rare high grade card with solid provenance will sell for a premium, conversely a card with a questionable or unknown background may sell for a discount.
Whether it all shakes out that way is uncertain; but what I feel pretty sure about is that we are going to see some major changes in the way cards are perceived in the near future. Once the greater hobby realizes the extent of problem cards that have been slabbed, there will be a major shift in the marketplace.
Cards perceived as problem free will continue to be in great demand, and the others will sell at deep discounts. What the hobby needs is more information, and I predict that is forthcoming.